Organic electroluminescent devices containing a near-infrared down-conversion layer

ABSTRACT

Embodiments of the disclosed subject matter provide a device having a substrate, at least one organic light-emitting layer disposed over the substrate, and at least one down-conversion layer. The at least one down-conversion layer may generate the NIR emission by absorbing at least a portion of the light emitted by the at least one organic light emitting layer, and re-emitting light at a longer NIR wavelength or range of wavelengths having a peak NIR emission that may be greater than 700 nm, greater than 750 nm, or greater than 800 nm. An out-of-plane optical density of the at least one down-conversion layer may be less than 0.1 for all wavelengths of light in a range from 400 nm to 600 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/597,648, filed Dec. 12, 2017, the entire contents of whichare incorporated herein by reference.

FIELD

The present invention relates to down-conversion structures for use inorganic light emitting diodes, and devices including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs. The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

According to an embodiment, an organic light emitting diode/device(OLED) is also provided. The OLED can include an anode, a cathode, andan organic layer, disposed between the anode and the cathode. Accordingto an embodiment, the organic light emitting device is incorporated intoone or more device selected from a consumer product, an electroniccomponent module, and/or a lighting panel.

According to embodiment of the disclosed subject matter, a device mayhave a substrate, at least one organic light-emitting layer disposedover the substrate, and at least one down-conversion layer. The at leastone down-conversion layer may generate the NIR emission by absorbing atleast a portion of the light emitted by the at least one organic lightemitting layer, and re-emitting light at a longer NIR wavelength orrange of wavelengths having a peak NIR emission that may be greater than700 nm, greater than 750 nm, or greater than 800 nm. An out-of-planeoptical density of the at least one down-conversion layer may be lessthan 0.1 for all wavelengths of light in a range from 400 nm to 600 nm.

The at least one down-conversion layer may be disposed over the at leastone light emitting layer. The out-of-plane optical density of the mostabsorptive of the at least one down-conversion layer may be between 0.01to 0.1, or the out-of-plane optical density may be a sum of the at leastone down-conversion layer that may be between 0.01 to 0.1. The at leastone down-conversion layer may have a transparency in the wavelengthrange of 400 nm to 600 nm, or 400 nm to 650 nm. An in-plane opticaldensity of a sum of the at least one down-conversion layer may begreater than 0.5, greater than 1, greater than 1.5, greater than 2,greater than 3, or greater than 5.

The at least one down-conversion layer may generate the NIR emission byabsorbing at least a portion of the light emitted by a red sub-pixel orNIR sub-pixel of a panel that includes the at least one organic lightemitting layer. The down-conversion layer may be selectively addressableby absorption of light emitted by a sub-pixel of a panel that includesthe at least one organic light-emitting layer with a peak wavelengthgreater than 650 nm.

The device may include a near-infrared (NIR) emitter disposed in the atleast one down-conversion layer has a concentration that is less than30% by volume, less than 20% by volume, or less than 10% by volume.

The at least one down-conversion layer may be selectively patterned overthe near-infrared (NIR) pixel or red sub-pixel of a panel including theat least one organic light emitting layer, and may generate the NIRemission by absorbing at least a portion of the light emitted by thenear-infrared (NIR) pixel or the red sub-pixel. The optical excitationof the at least one down-conversion layer may include a selectiveexcitation by an edge mounted light source. The at least one downconversion layer may include a near-infrared (NIR) emitter that isembedded into the waveguide or substrate which is photoexcited by theedge mounted light source.

The at least one down-conversion layer may produce at least a nearlyLambertian emission pattern. The at least one down-conversion layer maybe directionally enhanced to output non-Lambertian or highly-directionalemission. A size of the at least one down-conversion layer may be lessthan 110% of an area of any distinct sub-pixel, less than 105% of thearea of any distinct sub-pixel, or 100% of the area of any distinctsub-pixel.

According to an embodiment, a display device may include a plurality ofOLED pixels and sub-pixels, where less than 80%, less than 50%, lessthan 40%, or less than 30% of the plurality of OLED pixels have at leastone near infra-red (NIR) down-conversion layer disposed over a givensub-pixel such that emission is converted to NIR light, and theremaining pixels do not include the down conversion layer. In someembodiments, the given sub-pixel is an additional red sub-pixel ornear-infrared subpixel.

An out-of-plane optical density of the most absorptive of the at leastone NIR down-conversion layer may be between 0.01 to 0.1, and theout-of-plane optical density of a sum of the at least one NIRdown-conversion layer may be between 0.01 to 0.1 in a wavelength rangeselected from the group consisting of: 400 nm to 600 nm, 400 nm to 650nm, and 400 nm to 700 nm. At least a portion of the OLED pixels includesa red sub-pixel or near-infrared sub-pixel in an emissive stack with theat least one NIR down-conversion layer. An out-of-plane optical densityof a sum of the at least one NIR down-conversion layer may be greaterthan 0.5, greater than 1, or greater than 10. An out-of-plane opticaldensity of a sum of the at least one NIR down-conversion layer may beless than 0.5, less than 0.1, and less than 0.05. A near-infrared (NIR)emitter disposed in the NIR down-conversion layer may have aconcentration that is less than 30% by volume, less than 20% by volume,or less than 10% by volume.

According to an embodiment, display device may include a plurality ofOLED pixels and sub-pixels, where less than 80%, less than 50%, lessthan 40%, or less than 30% of the plurality of OLED pixels of thedisplay device have at least one down-conversion layer disposed over theplurality of pixels such that emission is converted to near infra-red(NIR) light, and the remaining pixels do not include the down-conversionlayer.

According to an embodiment, a device may include a substrate, an atleast one organic light-emitting layer disposed over the substrate, andat least one near-infrared (NIR) down-conversion layer disposed in astack with the at least one organic light emitting layer to generate NIRemission from light emitted by the OLED stack.

The at least one NIR down-conversion layer may shift one or morewavelengths of emissions from one or more red sub-pixels ornear-infrared (NIR) sub-pixels of the OLED stack. An out-of-planeoptical density of a sum of the at least one down-conversion layer maybe transmissive to a visible spectrum in the range that is greater than0.5, greater than 1, or greater than 5. A near-infrared (NIR) emitterdisposed in the at least one NIR down-conversion layer has aconcentration that may be less than 30% by volume, less than 20% byvolume, or less than 10% by volume. An in-plane optical density of a sumof the at least one NIR down-conversion layer may have an in-planeoptical density that is greater than 1.5, greater than 2, or greaterthan 3. An out-of-plane optical density of a sum of the at least one NIRdown-conversion layer may be less than 0.1 for light having a wavelengthrange from 400 nm to 600 nm. An optical excitation of the at least oneNIR down-conversion layer may include a selective excitation by an edgemounted light source. The at least one NIR down-conversion layer mayinclude an emitter that is optically excited by red or NIR light and hasan optical density in the red or NIR. The out-of-plane optical densityof the most absorptive of the at least one down-conversion layer may bebetween 0.01 to 0.1, or the out-of-plane optical density may be the sumof the at least one down-conversion layer is between 0.01 to 0.1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3A shows an example top emission or bottom emission OLED devicestructure that includes one or more NIR down-conversion layers accordingto embodiments of the disclosed subject matter.

FIG. 3B shows an example of a simplified structure of the OLED device ofFIG. 3A that includes one or more NIR down-conversion layers accordingto embodiments of the disclosed subject matter.

FIG. 4A shows a pixel structure having a placement for a NIRdown-conversion layer with blanket coverage of all pixels according toembodiments of the disclosed subject matter.

FIG. 4B shows a pixel structure having a placement for a NIRdown-conversion layer with selective coverage of the red subpixelaccording to embodiments of the disclosed subject matter.

FIG. 4C shows a pixel structure having a placement for a NIRdown-conversion layer with selective coverage of one of multipleindividually addressed red subpixels according to embodiments of thedisclosed subject matter.

FIG. 4D shows a pixel structure having a placement for a NIRdown-conversion layer with selective coverage of a NIR subpixelaccording to embodiments of the disclosed subject matter.

FIG. 5A shows an example configuration of a NIR down-conversion layer ona display face having a blanket coverage of a display according toembodiments of the disclosed subject matter.

FIG. 5B shows an example configuration of a NIR down-conversion layer ona display face having coverage of all or a fraction of a given subpixelon a display according to embodiments of the disclosed subject matter.

FIG. 5C shows an example configuration of a NIR down-conversion layer ona display face having selective regional coverage of a display accordingto embodiments of the disclosed subject matter.

FIG. 5D shows an example configuration of a NIR down-conversion layer ona display face having coverage of all or a fraction of a given subpixelon a region of a display according to embodiments of the disclosedsubject matter.

FIG. 6 shows a wave-guided excitation of a NIR down-conversion layer byedge-mounted excitation light sources according to embodiments of thedisclosed subject matter.

FIGS. 7A-7C show example configurations of NIR down-conversion layersdisposed over a portion of a display or particular sub-pixels accordingto embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. A consumer product comprising an OLED thatincludes the compound of the present disclosure in the organic layer inthe OLED is disclosed. Such consumer products would include any kind ofproducts that include one or more light source(s) and/or one or more ofsome type of visual displays. Some examples of such consumer productsinclude flat panel displays, computer monitors, medical monitors,televisions, billboards, lights for interior or exterior illuminationand/or signaling, heads-up displays, fully or partially transparentdisplays, flexible displays, laser printers, telephones, mobile phones,tablets, phablets, personal digital assistants (PDAs), wearable devices,laptop computers, digital cameras, camcorders, viewfinders,micro-displays (displays that are less than 2 inches diagonal), 3-Ddisplays, virtual reality or augmented reality displays, vehicles, videowalls comprising multiple displays tiled together, theater or stadiumscreen, and a sign. Various control mechanisms may be used to controldevices fabricated in accordance with the present invention, includingpassive matrix and active matrix. Many of the devices are intended foruse in a temperature range comfortable to humans, such as 18 C to 30 C,and more preferably at room temperature (20-25 C), but could be usedoutside this temperature range, for example, from −40 C to 80 C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

Implementations of the disclosed subject matter provide an emissivecolor filter layer, referred to as a down-conversion layer, to generatenear-infrared (NIR) emission from an organic electroluminescent device.Due to low emissive quantum yields and added challenges in devicefabrication, integration of NIR emitters within an OLED stack may notprove feasible. In implementations of the disclosed subject matter, NIRemission may be generated by the use of a down-conversion layer whichabsorbs a portion of the display electroluminescence and re-emits at alonger NIR wavelength.

Near-infrared (NIR) organic light-emitting diodes (OLEDs) may have anumber of applications including imaging, night vision, and medicaltherapies. However, producing NIR emission through directelectroluminescence may present significant challenges in low deviceefficiency and complication in the OLED stack fabrication. Many of theseissues may be mitigated by using an emissive color filter layer (e.g., adown-conversion layer) by which higher energy photons may be selectivelydown-converted to the NIR through absorption and emission. This layer,which can be deposited on the bottom or top of the OLED stack (e.g., theOLED stack shown in FIG. 3B), may be a NIR emitter layer or a NIRemitter doped within a selectively absorptive matrix. Examples of NIRemitters that may be used include a phosphorescent emitter, an organicfluorescent emitter, a quantum dot (QD), or a combination thereof.

FIG. 3A shows an example top emission or bottom emission OLED devicestructure that includes one or more NIR down-conversion layers accordingto embodiments of the disclosed subject matter. The OLED devicestructure may include an optional barrier layers or capping layers (CPL)that may be disposed on optional down-conversion layers (e.g., NIRdown-conversion layers). As shown in FIG. 3A, the barrier or CPL layersmay be interleaved with down-conversion layers. The OLED stack mayinclude a cathode that may be disposed on an electron injection layer(EIL). An electron transport layer (ETL) may be disposed on a blockinglayer (BL), an emissive layer (EML), and an electron blocking layer(EBL). A hole transport layer (HTL) may be disposed on a hole injectionlayer (HIL), an anode, an optional down-conversion layer, a substrate,an optional down-conversion layer, and an optional barrier layer orcapping layer.

FIG. 3B shows an example of a simplified structure of the OLED device ofFIG. 3A that includes one or more NIR down-conversion layers accordingto embodiments of the disclosed subject matter. An optionaldown-conversion layer may be disposed on an OLED stack (e.g., which mayinclude a cathode that may be disposed on an electron injection layer(EIL), an electron transport layer (ETL), a blocking layer (BL), anemissive layer (EML), an electron blocking layer (EBL), a hole transportlayer (HTL), a hole injection layer (HIL), and an anode). The OLED stackmay be disposed on an optional down-conversion layer, a substrate, andan optional down-conversion layer.

The NIR down-conversion layer as shown in FIGS. 3A-3B may act as: (1) aphotoswitchable pixel which depends on the emission spectrum of theunderlying OLED pixel(s), or as (2) a color-purifying layer whichredshifts the electroluminescent (EL) emission of a red pixel. In thefirst case, the layer absorption spectrum may be selected based on whichpixel and/or color is desired to turn the NIR emission on and off. Inthe second case, the layer absorption spectrum may act as a long-passfilter for a red or NIR pixel, selectively absorbing the high energyphotons of the red or NIR emitter/pixel and down-converting them to thedesired NIR region. The layer may emit deep enough in the NIR so as tonot present visible emission (e.g., emission having a wavelength between400 nm and 700 nm). The NIR down-conversion layer may preferably have apeak emission wavelength that is greater than 700 nm, more preferablygreater than 750 nm, and more preferably greater than 800 nm.

The configuration in the second case may allow for the process of NIRemission to depend on the absorption of EL emission from the OLEDemissive layer and the photoluminescence quantum yield (PLQY) of the NIRemitter. Selective absorption of EL photons by the NIR down-conversionlayer may be affected by the bandgap of the QD, organic, ororganometallic NIR emitter, as well as any absorptive host material theNIR emitter may be embedded in. This may allow for the down-conversionlayer to be transmissive to certain regions (e.g., the visible lightspectrum of 400 nm to 700 nm) which may prevent disruption of thevisible OLED operation. This may allow for switching of the NIR emissionbased on the emission of the OLED stack, or based on an emission of anexternal excitation source.

The transmission spectrum may determine the performance of the NIRdown-conversion layer. The layer thickness and the extinctioncoefficient of the contained materials in the NIR down-conversion layermay increase color purity and NIR down-conversion efficiency. In thecase of some organometallic emitters, such as platinum or iridium basedemitters, concentration quenching issues may need to be considered. Tominimize and/or prevent concentration quenching, the NIR emitter may bepresent in the down-conversion layer preferably at a concentration lessthan 30% by volume, more preferably less than 20% by volume, and morepreferably less than 10% by volume. In the case of a dendritic,polymeric, quantum dot, or excimer based emitter, concentrationquenching may not be an issue, or may be sufficiently avoidable withmolecular structure considerations (e.g. quantum dot ligand sphere). Ifthe down-conversion layer host material is non-absorptive in theexcitation region, for instance, when the layer is acting as adown-conversion color filter for a red or NIR pixel, the down-conversionlayer may absorb a sufficient amount of the excitation photons withoutgreatly increasing the NIR emitter concentration. For example, theout-of-plane optical density of the most absorptive of the at least onedown-conversion layer may be between 0.01 to 0.1, or the out-of-planeoptical density may be a sum of the at least one down-conversion layerthat may be between 0.01 to 0.1. The in-plane optical density of a sumof the at least one down-conversion layer may be greater than 0.5,greater than 1, greater than 1.5, greater than 2, greater than 3, orgreater than 5. In some implementations, the down-conversion layer mayhave an optical density in the photoexcitation region greater than 1.5,more preferably greater than 2, and more preferably greater than 3.

Optical excitation of the NIR emissive down-conversion layer may take ona variety of forms including: (1) broadband excitation by partialabsorption in the visible spectrum, (2) selective excitation by the redpixel and/or EML, (3) selective excitation by a NIR pixel and/or EML,and/or (4) selective excitation by an edge mounted waveguided lightsource such as an LED.

In case (1), the NIR down-conversion overlayer may be excited by one ormore pixels and/or EML layers, and may emit continuously so long as thedisplay is on in any form. A lower optical density layer may be used soas to partially filter the underlying visible emission. It may bepreferable that the down-conversion layer have an optical densitybetween 0.01 and 0.1. As this configuration may have indiscriminantphoton absorption, the broad above-bandgap absorption of a material likea quantum dot may be used.

In case (2), the NIR down-conversion overlayer may act to selectivelydown-convert photons from the red pixel or EML. It may be preferablethat the layer is partially absorptive with an optical density between0.01 and 0.1. To have selective absorption in the red, a material may beused with an absorption peak in the red without significant absorptionin the rest of the visible spectrum (e.g., 400 nm-700 nm), such as anorganic fluorophore.

Similarly to case (2), case (3) may use a material with a peakabsorption in the red-NIR region, such as an organic fluorophore. Inthis case, as the down-conversion layer may act to color shift a NIRpixel of higher than desired photon energy, the optical density may bepreferably greater than 1.5, more preferably greater than 2, and morepreferably greater than 3.

In case (4), the NIR down-conversion emitter is embedded in a waveguideor substrate layer which is photoexcited by one or multiple edge-mountedlight source(s) such as LEDs, as shown in FIG. 6. The down-conversionlayer may include a near-infrared (NIR) emitter that is embedded intothe waveguide or substrate which is photoexcited by the edge mountedlight source. The down-conversion layer should, therefore, be largelytransmissive to the visible with an OD preferably lower than 0.1 andmore preferably lower than 0.01 in the visible. In one embodiment ofthis case, the down-conversion emitter may be optically excited in thered-NIR and have an optical density in this region. The NIRdown-conversion layer may fully cover the display or be patterned inparticular regions so as to emit as several point sources (see, e.g.,FIGS. 5A-5D).

As shown in FIGS. 3A-3B, a device may have a substrate, at least oneorganic light-emitting layer disposed over the substrate (e.g., as partof an emissive layer (EML) as shown in FIG. 3A or as part of the OLEDstack shown in FIG. 3B), and at least one down-conversion layer. In someembodiments, the down-conversion lay may be disposed over the at leastone organic light emitting layer. As shown in FIGS. 3A-3B, one or moredown-conversion layers may be disposed above or below the OLED stack oremissive layer (EML). The at least one down-conversion layer maygenerate the NIR emission by absorbing at least a portion of the lightemitted by the at least one organic light emitting layer, andre-emitting light at a longer NIR wavelength or range of wavelengthshaving a peak NIR emission that may be greater than 700 nm, greater than750 nm, or greater than 800 nm.

The down-conversion layer may have an in-plane optical density and/or anout-of-plane optical density. As used throughout, both the out-of-planeand in-plane optical density may be the optical density determined byfirst measuring the ordinary (out-of-plane) and extraordinary (in-plane)extinction coefficient of a sample of the same composition as thedown-conversion layer by variable angle spectroscopic ellipsometry(VASE). The optical density may be calculated using the extinctioncoefficient obtained by VASE and the thickness of the film (forout-of-plane optical density), or the distance from the edge of thedisplay to the farthest most point of the down-conversion layerpatterned on the display (for in-plane optical density). Theout-of-plane optical density may also be measured by normal-incidencetransmission measurements on a sample of the same composition as thedown-conversion layer with thickness equal to that used in the device.An in-plane optical density of a sum of the at least one down-conversionmay be greater than 0.5, greater than 1, greater than 1.5, greater than2, greater than 3, or greater than 5. In some embodiments, anout-of-plane optical density of the at least one down-conversion layermay be less than 0.1 for all wavelengths of light in a range from 400 nmto 600 nm. The out-of-plane optical density of the most absorptive ofthe at least one down-conversion layer may be between 0.01 and 0.1. Insome embodiments, the out-of-plane optical density may be the sum of theat least one down-conversion layer that may be between 0.01 and 0.1.

The at least one down-conversion layer may have a transparency in thewavelength range of 400 nm to 600 nm, or 400 nm to 650 nm. As generallyused throughout, transparency of the down-conversion layer may allow forat least 90% of light within the visible range of 400 nm to 600 nm to betransmitted. The transparency of the down-conversion layer shown inFIGS. 7B-7C and discussed below may desirably have less than 90%transmittance for light within the visible range of 400 nm to 600 nm.

The at least one down-conversion layer may generate the NIR emission byabsorbing at least a portion of the light emitted by a red sub-pixel orNIR sub-pixel of a panel that includes the at least one organic lightemitting layer. The panel may be part of a display device. Thedown-conversion layer may be selectively addressable by absorption oflight emitted by a sub-pixel of a panel that includes the at least oneorganic light-emitting layer with a peak wavelength greater than 650 nm.

In some embodiments, the device may include a near-infrared (NIR)emitter disposed in the at least one down-conversion layer has aconcentration that is less than 30% by volume, less than 20% by volume,or less than 10% by volume.

The at least one down-conversion layer may be selectively patterned overthe near-infrared (NIR) pixel or red sub-pixel of a panel including theat least one organic light emitting layer, and may generate the NIRemission by absorbing at least a portion of the light emitted by thenear-infrared (NIR) pixel or the red sub-pixel. The NIR pixel or redsub-pixel may be part of the emissive layer (EML) shown in FIG. 3A, theOLED stack shown in FIG. 3B, and/or the pixels and/or sub-pixels shownin FIGS. 4A-4D.

The at least one down-conversion layer may include an emitter that isoptically excited by light of a red or near-infrared (NIR) spectrum. Forexample, the down-conversion layers shown in FIGS. 3A-3B and/or FIGS.4A-4D may include an emitter that is optically excited by light of a redor near-infrared (NIR) spectrum (e.g., such as light emitted from a redsub-pixel NIR sub-pixel).

FIGS. 4A-4D show pixel and/or subpixel configurations for the NIR colorfilter layer. FIG. 4A shows blanket coverage of all pixels, FIG. 4Bshows selective coverage of a red subpixel, FIG. 4C shows selectivecoverage of one of multiple individually addressed red subpixels, andFIG. 4D shows selective coverage of a NIR subpixel. The exampleconfigurations shown in FIGS. 4A-4B provide continuous NIR emission froma given pixel whenever it is on. The configurations shown in FIGS. 4C-4Dprovide for individual NIR pixel addressing, which may be advantageouswhen separately controllable NIR emission or emission in the absence ofvisible light is desired.

These individual NIR down-conversion layer subpixel designs may beapplied selectively on a greater display, as shown in FIGS. 5A-5D. Thesubpixel pattern shown in FIGS. 4A-4D may be applied to the wholedisplay (e.g., a blanket cover of a display, as shown in FIG. 5A), allor a fraction of a given subpixel (e.g., coverage of all or a fractionof a given subpixel on a display, as shown in FIG. 5B), a whole region(e.g., a selective regional coverage of a display, as shown in FIG. 5C)or all or a fraction of subpixels in a given region (e.g., coverage ofall or a fraction of a subpixel on a region, as shown in FIG. 5D).Partial coverage may provide on-off control of the NIR emission, as wellas fine tuning of the NIR brightness. The partial coverable may provideless reduction of the underlying subpixel efficiency (e.g., in the caseof R (red), G (green), or B (blue) NIR photoexcitation).

According to an embodiment, a display device may include a plurality ofOLED pixels and sub-pixels, where less than 80%, less than 50%, lessthan 40%, or less than 30% of the plurality of OLED pixels have at leastone down-conversion layer disposed over a given sub-pixel such thatemission may be converted to near infra-red (NIR) light, and theremaining pixels do not include the down-conversion layer (see, e.g.,FIG. 7C). In some implementations, the given sub-pixel may be anadditional red sub-pixel or a near-infrared sub-pixel (see, e.g., FIG.7B). An out-of-plane optical density of the most absorptive of the atleast one down-conversion layer is between 0.01 to 0.1, and theout-of-plane optical density of a sum of the at least onedown-conversion layer is between 0.01 to 0.1 in a wavelength range whichmay be 400 nm to 600 nm, 400 nm to 650 nm, or 400 nm to 700 nm. At leasta portion of the OLED pixels includes a red sub-pixel or near-infraredsub-pixel in an emissive stack with the at least one down-conversionlayer (see, e.g., FIGS. 3A-3B and FIGS. 4A-4D). An out-of-plane opticaldensity of a sum of the at least one down-conversion layer may begreater than 0.5, greater than 1, or greater than 10. An out-of-planeoptical density of a sum of the at least one down-conversion layer maybe less than 0.5, less than 0.1, or less than 0.05. A near-infrared(NIR) emitter disposed in the down-conversion layer may have aconcentration that is less than 30% by volume, less than 20% by volume,or less than 10% by volume.

According to an embodiment, a device may include a substrate, an atleast one organic light-emitting layer disposed over the substrate, andat least one near-infrared (NIR) down-conversion layer disposed in astack with the at least one organic light emitting layer to generate NIRemission from light emitted by the OLED stack. The features of thisembodiment may be shown, for example, in FIGS. 3A-3B.

In these embodiments, the at least one NIR down-conversion layer mayshift one or more wavelengths of emissions from one or more redsub-pixels or near-infrared (NIR) sub-pixels (as shown, e.g., in FIGS.4A-4D) of the OLED stack (as shown, e.g., in FIG. 3B). An out-of-planeoptical density of a sum of the at least one down-conversion layer maybe transmissive to a visible spectrum in the range that is greater than0.5, greater than 1, or greater than 5. A NIR emitter disposed in the atleast one NIR down-conversion layer as shown in FIGS. 4A-4D may have aconcentration that may be less than 30% by volume, less than 20% byvolume, or less than 10% by volume. An in-plane optical density of a sumof the at least one NIR down-conversion may be greater than 1.5, greaterthan 2, or greater than 3. An out-of-plane optical density of a sum ofthe at least one NIR down-conversion layer may be less than 0.1 forlight having a wavelength range from 400 nm to 600 nm. The at least oneNIR down-conversion layer may include an emitter that is opticallyexcited by red or NIR light. The out-of-plane optical density of themost absorptive of the at least one down-conversion layer may be between0.01 and 0.1, or the out-of-plane optical density may be the sum of theat least one down-conversion layer is between 0.01 and 0.1.

FIGS. 7A-7C show example configurations of NIR down-conversion layersdisposed over a portion of a display or particular sub-pixels accordingto embodiments of the disclosed subject matter. FIG. 7A shows a displaydevice having a plurality of OLED pixels and sub-pixels, where less than80% of the plurality of OLED pixels of the display device have at leastone down-conversion layer disposed over the plurality of pixels suchthat emission is converted to near infra-red (NIR) light, and theremaining pixels do not include the down-conversion layer. FIG. 7B showsa display device having a plurality of OLED pixels and sub-pixels, whereless than 80% of the plurality of OLED pixels have at least onedown-conversion layer disposed over an additional red sub-pixel ornear-infrared subpixel such that emission is converted to near infra-red(NIR) light, and the remaining pixels do not include the down-conversionlayer. FIG. 7C shows a display device having a plurality of OLED pixelsand sub-pixels, where less than 80% of the plurality of OLED pixels haveat least one down-conversion layer disposed over a given sub-pixel suchthat emission is converted to near infra-red (NIR) light, and theremaining pixels do not include the down-conversion layer. In someembodiments of the examples shown in FIGS. 7A and 7C, less than 50% ofthe plurality of OLED pixels may have at least one down-conversion layerdisposed over a given sub-pixel such that emission may be converted tonear infra-red (NIR) light, and the remaining pixels do not include thedown-conversion layer. In other embodiments, less than 40% or less than30% of the plurality of OLED pixels may have at least onedown-conversion layer disposed over a given sub-pixel such that emissionmay be converted to near infra-red (NIR) light. In the examples shown inFIGS. 7B-7C, it may be desirable for a peak optical density of the NIRdown conversion layers to be greater than 0.5, greater than 1.0, greaterthan 1.5, and the like for light having a wavelength range from 400 nmto 800 nm.

In general, the placement of the color down-conversion filter (e.g., adown-conversion layer) at the exterior of the device may produce aLambertian or nearly Lambertian emission pattern. In some embodiments,the emission pattern may be independent of the emission pattern of theunderlying OLED device stack (e.g., the OLED stack shown in FIG. 3B). Insome embodiments, the at least one down-conversion layer may produce atleast a nearly Lambertian emission pattern that is independent of theemission pattern of the at least one organic light emitting layer.

In the case where the near-infrared pixel is used for broad illumination(e.g., for retinal tracking), this Lambertian pattern may be desirable.When non-Lambertian or highly directional emission is desired, the colorfilter layer (e.g., the down-conversion layer(s) shown in FIGS. 3A-3B)may be directionally enhanced by, for example, utilization of aplasmonic perforated metal film. That is, at least one down-conversionlayer may be directionally enhanced to output non-Lambertian orhighly-directional emission. This may be applicable when the NIRdown-conversion layer is selectively patterned, rather than covering theRGB pixels, so as to avoid any disruption of the RGB emission pattern.When selectively patterned, the spatial overlap of the color filterlayer (e.g., the down conversion layer(s)) with any distinct subpixelmay be considered. A size of the color filter layer (e.g., thedown-conversion layer(s)) may be less than 110% of an area of anydistinct sub-pixel, less than 105% of the area of any distinctsub-pixel, or 100% of the area of any distinct sub-pixel.

In some embodiments, the OLED has one or more characteristics selectedfrom the group consisting of being flexible, being rollable, beingfoldable, being stretchable, and being curved. In some embodiments, theOLED is transparent or semi-transparent. In some embodiments, the OLEDfurther comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising adelayed fluorescent emitter. In some embodiments, the OLED comprises aRGB pixel arrangement or white plus color filter pixel arrangement. Insome embodiments, the OLED is a mobile device, a hand held device, or awearable device. In some embodiments, the OLED is a display panel havingless than 10 inch diagonal or 50 square inch area. In some embodiments,the OLED is a display panel having at least 10 inch diagonal or 50square inch area. In some embodiments, the OLED is a lighting panel.

In some embodiments of the emissive region, the emissive region furthercomprises a host.

In some embodiments, the compound can be an emissive dopant. In someembodiments, the compound can produce emissions via phosphorescence,fluorescence, thermally activated delayed fluorescence, i.e., TADF (alsoreferred to as E-type delayed fluorescence), triplet-tripletannihilation, or combinations of these processes.

The OLED disclosed herein can be incorporated into one or more of aconsumer product, an electronic component module, and a lighting panel.The organic layer can be an emissive layer and the compound can be anemissive dopant in some embodiments, while the compound can be anon-emissive dopant in other embodiments.

The organic layer can also include a host. In some embodiments, two ormore hosts are preferred. In some embodiments, the hosts used may be a)bipolar, b) electron transporting, c) hole transporting or d) wide bandgap materials that play little role in charge transport. In someembodiments, the host can include a metal complex. The host can be aninorganic compound.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Various materials may be used for the various emissive and non-emissivelayers and arrangements disclosed herein. Examples of suitable materialsare disclosed in U.S. Patent Application Publication No. 2017/0229663,which is incorporated by reference in its entirety.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the HBL interface.

ETL:

An electron transport layer (ETL) may include a material capable oftransporting electrons. The electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A device comprising: a substrate; at least one organiclight-emitting layer disposed over the substrate; at least onedown-conversion layer, wherein the at least one down-conversion layergenerates NIR emission by absorbing at least a portion of the lightemitted by the at least one organic light emitting layer, andre-emitting light at a longer NIR wavelength or range of wavelengthshaving a peak NIR emission that is greater than at least one selectedfrom the group consisting of: 700 nm, 750 nm, and 800 nm, and wherein anout-of-plane optical density of the at least one down-conversion layeris selected from at least one from the group consisting of: between 0.01and 0.1, and between 0.001 and 0.1 for all wavelengths of light in arange from 400 nm to 600 nm.
 2. The device of claim 1, wherein the atleast one down-conversion layer is disposed over the at least one lightemitting layer.
 3. The device of claim 1, wherein the out-of-planeoptical density is selected from the group consisting of: theout-of-plane optical density of the most absorptive of the at least onedown-conversion layer is between 0.01 to 0.1, and the out-of-planeoptical density of a sum of the at least one down-conversion layer isbetween 0.01 to 0.1.
 4. The device of claim 1, wherein the at least onedown-conversion layer has transparency in the wavelength range selectedfrom the group consisting of: 400 nm to 600 nm, and 400 nm to 650 nm. 5.The device of claim 1, wherein an in-plane optical density of a sum ofthe at least one down-conversion layer is selected from the groupconsisting of: between 0.5 and 5, and between 5-10, between 10-100, andbetween 100-1000.
 6. The device of claim 1, wherein the at least onedown-conversion layer generates the NIR emission by absorbing at least aportion of the light emitted by a red sub-pixel or NIR sub-pixel of apanel that includes the at least one organic light emitting layer. 7.The device of claim 1, wherein the down-conversion layer is selectivelyaddressable by absorption of light emitted by a sub-pixel of a panelthat includes the at least one organic light-emitting layer with a peakwavelength between 650-1000 nm.
 8. The device of claim 1, wherein the atleast one down-conversion layer is selectively patterned over anear-infrared (NIR) pixel or red sub-pixel of a panel including the atleast one organic light emitting layer, and generates the NIR emissionby absorbing at least a portion of the light emitted by thenear-infrared (NIR) pixel or the red sub-pixel.
 9. The device of claim1, wherein optical excitation of the at least one down-conversion layerincludes a selective excitation by an edge mounted light source.
 10. Thedevice of claim 9, wherein the at least one down-conversion layerincludes a near-infrared (NIR) emitter that is embedded into a waveguideor the substrate which is photoexcited by the edge mounted light source.11. The device of claim 1, wherein the at least one down-conversionlayer produces at least a nearly Lambertian emission pattern.
 12. Thedevice of claim 1, wherein the at least one down-conversion layer isdirectionally enhanced to output non-Lambertian or highly-directionalemission.
 13. The device of claim 1, wherein a size of the at least onedown-conversion layer is selected from the group consisting of: lessthan 110% of an area of any distinct sub-pixel, less than 105% of thearea of any distinct sub-pixel, and 100% of the area of any distinctsub-pixel.
 14. A display device comprising a plurality of OLED pixelsand sub-pixels, wherein a percentage of the plurality of OLED pixels isless than one selected from a group consisting of: 80%, 50%, 40%, and30% of the plurality of OLED pixels have at least one near infra-red(NIR) down-conversion layer disposed over a given sub-pixel such thatemission is converted to NIR light, and the remaining pixels do notinclude the down-conversion layer, wherein an out-of-plane opticaldensity of a sum of the at least one NIR down-conversion layer isselected from the group consisting of: between 0.5-10, and between10-20, and between 20-100.
 15. The display device of claim 14, whereinthe given sub-pixel is an additional red sub-pixel or near-infraredsub-pixel.
 16. The display device of claim 14, wherein an out-of-planeoptical density of the most absorptive of the at least one NIRdown-conversion layer is between 0.01 to 0.1, and the out-of-planeoptical density of a sum of the at least one NIR down-conversion layeris between 0.01 to 0.1 in a wavelength range selected from the groupconsisting of: 400 nm to 600 nm, 400 nm to 650 nm, and 400 nm to 700 nm.17. The display device of claim 14, wherein at least a portion of theOLED pixels includes a red sub-pixel or near-infrared sub-pixel in anemissive stack with the at least one NIR down-conversion layer.
 18. Thedisplay device of claim 14, wherein an out-of-plane optical density of asum of the at least one NIR down-conversion layer is selected from thegroup consisting of: between 0.01-0.05, between 0.01 and 0.1, andbetween 0.001 and 0.1.
 19. A device comprising: a substrate; an at leastone organic light-emitting layer disposed over the substrate; and atleast one near-infrared (NIR) down-conversion layer disposed in a stackwith the at least one organic light emitting layer to generate NIRemission from light emitted by the stack, wherein the at least one NIRdown-conversion layer shifts one or more wavelengths of emissions fromone or more red sub-pixels or near-infrared (NIR) sub-pixels of thestack, and wherein an out-of-plane optical density of a sum of the atleast one NIR down-conversion layer is selected from the groupconsisting of: between 0.5-10, and between 10-20, and between 20-100.